1. Field of the Invention
The present invention relates in general to power slide doors of a motor vehicle, and more particularly to drive devices for driving the slide doors.
2. Description of the Prior Art
In order to clarify the task of the present invention, one conventional drive device of an automotive slide door will be described, which is disclosed in Japanese Patent First Provisional Publication No. 61-36480.
The conventional door drive device comprises generally a drive cable which extends around a given oval path defined beneath a vehicle floor, several pulleys around which the drive cable is put, a drive drum which has both ends of the drive cable wound therearound, and a reversible motor which drives the drive drum. An electromagnetic clutch and a speed reduction gear are arranged between the drive drum and the motor. The drive cable is fixed to the door at a portion.
Thus, when, with the clutch being engaged, the motor is energized to run in a given direction, the drive drum is rotated to drive the drive cable. With this, the door is moved forward or rearward.
The reason of using the clutch between the drive drum and the speed reduction gear is to facilitate a movement of the door effected by manual labor. That is, when the door drive device gets out of order, the clutch is switched to assume its disengaged condition. Under this condition, the rotation of the drive drum carried out by manual movement of the door does not affect the speed reduction gear and the motor. If the manual movement of the door is carried out with the clutch kept engaged, a great resistance against the movement is produced by these devices.
However, the above-mentioned conventional door slide device has the following drawbacks due to its inherent construction.
First, by using the electromagnetic clutch, the door drive device becomes bulky, heavy, and costly.
Second, combining the above-mentioned door drive device with other door control devices such as those disclosed in Japanese Patent First Provisional Publication No. 1-164647 is difficult. The devices disclosed in Japanese Publication 1-164647 are an automatic door closure which forces the door to shift to a fully closed latched position when the door comes to a half-latch position, and a door lock canceller which forces the latched condition of the closed door to be canceled prior to starting the opening movement of the door. In fact, it is difficult to obtain timed operations for all of these control devices. For example, if the door drive device starts to operate prior to cancelling the latched condition of the door, a great load is applied to the cable, the speed reduction gear and the motor. Furthermore, if, upon closing of the door, the speed at which the door is shifted by the door closure device, and the speed at which the door is moved by the door drive device, are not matched, an excessive load is applied to both the door closure device and the door drive device.